Rigidly Contorted Polyamide Membranes Based on Spirofluorene Monomers for Efficient Nanofiltration

The cross-linking density of interfacial polymerization-based nanofiltration (NF) membranes can be tuned to meet the requirements of diverse applications. Selecting monomers with distinct structures and reactivities enables precise control over key separation properties such as pore size and porosity. In this study, a thin-film composite nanofiltration membrane (TFC-NF) was prepared through interfacial polymerization (IP) by introducing 2,2′,7,7′-Tetraamino-9,9′-spirobifluorene (TASBF) has a near-tetrahedral geometry that effectively suppresses dense packing of polyamide chains. At the same time, its rigid aromatic backbone promotes ordered molecular stacking through π–π interactions. By systematically tuning key parameters such as monomer concentration and interfacial polymerization time, the optimal fabrication conditions for the membrane were identified. Under optimized conditions, the membrane achieved a high pure water flux of 13.50 L·m –2 ·h –1 ·bar –1 with a molecular weight cutoff (MWCO) of 534 Da. It exhibited high rejection (>99%) toward various dyes, enabling efficient recovery of dyes from saline wastewater. In pharmaceutical desalting applications, the membrane retained over 90% of multiple model drugs and demonstrated excellent operational stability. The fabricated TFC membranes show broad application prospects in practical scenarios such as textile dyeing wastewater resource recovery and pharmaceutical desalination.